Abstract
Computed tomography (CT), combined positron emitted tomography and CT (PET/CT), and magnetic resonance imaging (MRI) are commonly used in head and neck radiation planning. Hybrid PET/MRI has garnered attention for potential added value in cancer staging and treatment planning. Herein, we compare PET/MRI vs. planning CT for head and neck cancer gross tumor volume (GTV) delineation. We prospectively enrolled patients with head and neck cancer treated with definitive chemoradiation to 60-70 Gy using IMRT. We performed pretreatment contrast-enhanced planning CT and gadolinium-enhanced PET/MRI. Primary and nodal volumes were delineated on planning CT (GTV-CT) prospectively before treatment and PET/MRI (GTV-PET/MRI) retrospectively after treatment. GTV-PET/MRI was compared to GTV-CT using separate rigid registrations for each tumor volume. The Dice similarity coefficient (DSC) metric evaluating spatial overlap and modified Hausdorff distance (mHD) evaluating mean orthogonal distance difference were calculated. Minimum dose to 95% of GTVs (D95) was compared. Eleven patients were evaluable (10 oropharynx, 1 larynx). Nine patients had evaluable primary tumor GTVs and seven patients had evaluable nodal GTVs. Mean primary GTV-CT and GTV-PET/MRI size were 13.2 and 14.3 cc, with mean intersection 8.7 cc, DSC 0.63, and mHD 1.6 mm. D95 was 65.3 Gy for primary GTV-CT vs. 65.2 Gy for primary GTV-PET/MRI. Mean nodal GTV-CT and GTV-PET/MRI size were 19.0 and 23.0 cc, with mean intersection 14.4 cc, DSC 0.69, and mHD 2.3 mm. D95 was 62.3 Gy for both nodal GTV-CT and GTV-PET/MRI. In this series of patients with head and neck (primarily oropharynx) cancer, PET/MRI and CT-GTVs had similar volumes (though there were individual cases with larger differences) with overall small discrepancies in spatial overlap, small mean orthogonal distance differences, and similar radiation doses.
Highlights
Head and neck radiation oncologists routinely utilize computed tomography (CT), combined positron emitted tomography and CT (PET/CT), and magnetic resonance imaging (MRI) for staging, treatment planning, and assessment of disease response
gross target volume (GTV) generated by both imaging modalities were similar in size, with mean primary GTV of 13.2 and 14.3 cc (p = 0.82) and mean nodal GTV of 19.0 and 23.0 cc (p = 0.94), for CT and PET/MRI, respectively
We assessed volumetric differences in GTVs delineated using routine contrast-enhanced planning CT vs. gadolinium-enhanced PET/MRI, as well as differences in dose received by these volumes after treatment based on planning CT alone
Summary
Head and neck radiation oncologists routinely utilize computed tomography (CT), combined positron emitted tomography and CT (PET/CT), and magnetic resonance imaging (MRI) for staging, treatment planning, and assessment of disease response. PET/ CT has been shown to be superior to CT alone in staging head and neck cancer, with better sensitivity for nodal disease as well as distant metastases [1,2,3]. Diffusion-weighted MRI imaging has been investigated as a method of increasing specificity for detection of nodal metastases and may add further benefit [9]. The advantages of both PET/CT and MRI over CT alone have led to research into the role of hybrid PET/MRI imaging. This technology allows for simultaneous data acquisition resulting in optimal spatial and temporal co-registration of structural, functional, and molecular image data
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